A fish market in Tokyo. A farmers market in Iowa. A stock exchange in London. An online marketplace where a buyer in Lagos purchases a handbag from a seller in Milan. A market is any system where buyers and sellers exchange goods, services, or resources. It does not need a physical location. It needs rules, information, and a way to settle transactions.

Markets vary enormously in structure. Some are highly competitive, with thousands of sellers offering identical products. Others are dominated by a handful of firms or a single monopolist. Some are regulated heavily. Others operate in a gray zone. The structure determines how prices are set, how much choice buyers have, and how much profit sellers can earn.

Prices coordinate activity in a market without anyone directing it. When copper gets scarce, its price rises. That tells producers to mine more and consumers to use less. No central planner issues the order. The price does the work. Economist Friedrich Hayek called this spontaneous order, and it remains one of the most powerful ideas in the field.

Market structures

• Perfect competition: many sellers, identical products
• Monopolistic competition: many sellers, differentiated products
• Oligopoly: a few large sellers
• Monopoly: a single seller